1014. A novel approach for differentiating Escherichia coli and Shigella species by MALDI-TOF mass spectrometry
Session: Poster Abstract Session: Detecting, Identifying, and Typing Bacteria
Saturday, October 22, 2011
Room: Poster Hall B1
Background: Shigella species are responsible for shigellosis (bacillary dysentery) and some strains can cause life-threatening dysentery. Escherichia coli is closely related to Shigella spp. and patient isolates may be commensal or pathogenic. Variants of E. coli termed “inactive” are biochemically very similar to Shigella spp. but their pathogenic potential is controversial. Current identification methods based on biochemical tests are time consuming and often inconclusive. Neither sequencing the 16S rRNA gene nor routine matrix-assisted laser desorption/ionization - time of flight mass spectrometry (MALDI-TOF MS) can reliably differentiate between Shigella spp. and E. coli. We have used a biomarker discovery approach to identify signature peaks that distinguish E. coli and Shigella species using a rapid, inexpensive MALDI-TOF MS method.

Methods: 112 clinical isolates including 46 Shigella spp. (29 S. sonnei, 15 S. flexneri, 2 S. boydii) and 66 E. coli (28 typical and 38 inactive) were chosen for analysis with MALDI-TOF MS. Spectral profiles from triplicate extracts of each isolate were collected using a microflex LRF MALDI-TOF mass spectrometer with MALDI Biotyper software (Bruker Daltonics). Isolates were grouped by phenotype or species for statistical analysis and identification of distinguishing peaks using ClinPro Tools and flexanalysis software (Bruker Daltonics).

Results: A total of 336 spectra were generated from 112 isolates, and each spectrum contained approximately 135 peaks. Pair wise comparisons of all isolate categories revealed several candidate peaks that showed statistically significant differences between categories. Candidate peaks were manually analyzed using flexanalysis to calculate the frequency at which each peak occurred in each isolate category. This analysis identified at least 7 peaks that can distinguish among the Shigella and E. coli isolates examined.

Conclusion: Using these newly discovered discriminatory markers, MALDI-TOF MS could offer an inexpensive, fast and novel approach for differentiating E. coli from Shigella species.

Subject Category: D. Diagnostic microbiology

Prasanna Khot, PhD, Clinical Microbiology, ARUP Laboratories, Salt Lake City, UT, Ann Croft, Bacteriology, ARUP Laboratories, Salt Lake City, UT and Mark A. Fisher, Ph.D., D(ABMM), Bacteriology, Antimicrobials, ID Rapid Testing and Parasitology, ARUP Laboratories, Salt Lake City, UT


P. Khot, None

A. Croft, None

M. A. Fisher, None

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.